The present application relates to an optical element and a method for making the same, a master and a method for making the same, and a display apparatus. In particular, it relates to an optical element provided with a hard coat layer.
In recent years, various display apparatuses such as liquid crystal displays (LCDs) and plasma display panels (PDPs) have become increasingly popular. When outside light such as sun light or indoor illumination cast glares on screens of such display apparatuses, visibility in daylight is significantly obstructed; thus, optical films such as antiglare films that diffuse and reflect the outside light at screen surfaces are used extensively.
Heretofore, a technique of forming fine irregularities on surfaces of these optical films has been employed to diffusely reflect outside light at the screen surfaces. To be more specific, the mainstream practice for current liquid crystal display apparatuses is to form a diffusing layer on a transparent plastic substrate by application considering a scratch property, the diffusing layer being composed of a hard-coat coating and transparent fine particles dispersed in the coating.
However, improvements in image quality and resolution of the above-mentioned various display apparatuses represented by recent flat-screen televisions are rapidly progressing and pixels are increasingly becoming smaller in size. As a result, light transmitting through an optical film is distorted by refraction or diffusion by fine particles in an antiglare layer or surface irregularities, leading to problems such as unclear images, glares caused by varying luminance, whitening of surfaces, and significant deterioration of image quality caused thereby. Accordingly, current optical films in which surface irregularities are formed by using fine particles are not compatible to the above-described improvements in the image quality and resolution. Thus, an optical film that has surface irregularities without using fine particles is desired.
Heretofore, in order to diffusely reflect outside light at screen surfaces, a technique of forming fine irregularities by embossing (shape transfer) has been studied as a technique for forming fine irregularities on a surface, as shown in Japanese Examined Patent Application Publication No. 4-59605, Japanese Patent No. 3374299, Japanese Unexamined Patent Application Publication No. 2004-29240, and Japanese Unexamined Patent Application Publication No. 2005-156615.
Japanese Examined Patent Application Publication No. 4-59605 proposes a method for forming a high-definition, non-reflective polarizer, the method including forming fine irregular rough surface in a polarizer-protecting film surface of a cellulose-based plastic by embossing and then partly dissolving a surface layer of the fine irregular rough surface with an organic solvent.
Japanese Patent No. 3374299 proposes a method for producing an antiglare film, the method including forming a coarse irregular layer composed of an ionization radiation-curable resin and forming fine irregularities along the surface of the coarse irregular layer. According to this production method, coarse irregularities are formed by one of an embossing technique, a sand-blasting technique, and a resin-convection technique under drying, and fine irregularities are formed by using a thin-film coating layer or by utilizing a lifting effect.
Japanese Unexamined Patent Application Publication No. 2004-29240 proposes a method for producing an antireflection film, involving imparting irregularities to a film surface by embossing. According to this production method, the arithmetic mean roughness of the irregularities of a template used for embossing is set to 0.05 μm or more and 2.00 μm or less and the average period of the irregularities is set to 50 μm or less.
Japanese Unexamined Patent Application Publication No. 2005-156615 proposes a method for producing an antiglare film, the method including stretching a film with a tenter before or after irregularities are formed on the film surface by pressing the film surface of a template during the step of forming a thermoplastic resin film and forming a hard coat layer on the resulting irregular surface.